psql \copy hanging

Hi list

On Windows, I have an unattended script that exports data overnight by
issuing psql commands like :
psql -f mycommands.sql
whith mycommands.sql containing a bunch of \copy lines like :
\copy (SELECT * FROM someview) TO
'\\windowsserver\windowsshare\somefile.csv'

When I run this script by hand, everything is fine but when it runs
overnight it hangs and allways on the same line.
There is no lock in the database, and the connection is marked as active
in the backend and running the statement "COPY (SELECT * FROM myview) TO
STDOUT".
So where can things be hanging ?
My first guess (appart from db lock) was that the target file was locked
by the filesystem. But wouldn't psql know about it and fail with an error ?

Thanks for your help !

--
Arnaud